EVAL-ADM1023EB ON Semiconductor, EVAL-ADM1023EB Datasheet - Page 8

• Manufacturer Part Number: EVAL-ADM1023EB
• Description: BOARD EVAL FOR ADM1023
• Manufacturer: ON Semiconductor
• Type: Temperature Sensorr

Specifications of EVAL-ADM1023EB

• Contents: Evaluation Board
• For Use With/related Products: ADM1023
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

operating currents of I and NI. The resulting waveform is
passed through a low−pass filter to remove noise, then to a
chopper−stabilized amplifier that performs the functions of
amplification and rectification of the waveform to produce
a dc voltage proportional to DV
by the ADC, which gives a temperature output in binary
format. To further reduce the effects of noise, digital filtering
is performed by averaging the results of 16 measurement
cycles. Signal conditioning and measurement of the internal
temperature sensor are performed in a similar manner.
measure the output of an external temperature sensor. This
figure shows the external sensor as a substrate PNP
transistor, provided for temperature monitoring on some
microprocessors, but it could equally well be a discrete
transistor. If a discrete transistor is used, the collector is not
grounded and should be connected to the base. To prevent
ground noise from interfering with the measurement, the
more negative terminal of the sensor is not referenced to
ground but is biased above ground by an internal diode at the
D− input. If the sensor is operating in a noisy environment,
C1 may optionally be added as a noise filter. Its value is
1000 pF maximum. See the Layout Considerations section
for more information on C1.
Sources of Errors on Thermal Transistors
Measurement Method; The Effect of Ideality Factor (n)
temperature measured by a thermal transistor are described in
this section. For a thermal transistor implemented on a
submicron process, such as the substrate PNP used on a
Pentium III processor, the temperature errors due to the
combined effect of the ideality factor and beta are shown to
be less than 3°C. Equation 2 is optimized for a substrate PNP
transistor (used as a thermal diode) usually found on CPUs
designed on submicron CMOS processes such as the Pentium
III processor. There is a thermal diode on board each of these
processors. The n in Equation 2 represents the ideality factor
of this thermal diode. This ideality factor is a measure of the
deviation of the thermal diode from ideal behavior.
specifications, measured values of n at 100°C are:
when calculating temperature T
n
This is given by:
where:
To measure DV
Figure 13 shows the input signal conditioning used to
The effects of ideality factor (n) and beta (b) of the
According to Pentium III processor manufacturing
MIN
The ADM1023 takes this ideality factor into consideration
K is Boltzmann’s constant.
q is the charge on the electron (1.6 × 10
T is the absolute temperature in Kelvins.
N is the ratio of the two collector currents.
n is the ideality factor of the thermal diode (TD).
+ 1.0057 t n
DV
BE
TYPICAL
BE
, the sensor is switched between
+ nKT
+ 1.008 t n
q
BE
TD
. This voltage is measured
of the thermal diode. The
1n ( N )
+ 1.0125
MAX
–19
Coulombs).
http://onsemi.com
(eq. 2)
(eq. 3)
ADM1023
8
ADM1023 is optimized for n
on n from this typical value causes a temperature error that is
calculated below for the n
processor at T
thermal diode for a Pentium III processor is about 2.5°C.
diode measurement due to deviations on n from its typical
value is given by:
Beta of Thermal Transistor
transistor where the emitter current is forced into the device.
The derivation of Equation 2 assumed that the collector
currents were scaled by N as the emitter currents were also
scaled by N. Thus, this assumes that beta (b) of the transistor
is constant for various collector currents. Figure 14 shows
typical b variation vs. collector current for Pentium III
processors at 100°C. The maximum b is 4.5 and varies less
than 1% over the collector current range from 7 mA to
300 mA.
current.
factor, n, and beta, b yields:
temperature errors of less than 0.4°C.
DT
DT
DT + n * 1.008
Thus, the temperature error due to variation on n of the
In general, this additional temperature error of the thermal
In Figure 13, the thermal diode is a substrate PNP
Expressing the collector current in terms of the emitter
Rewriting the equation for DV
All b variations of less than 1% (e < 0.01) contribute to
b
MIN
MAX
Figure 14. Variation of
MAX
where T
where:
b
< 4.5
+ 1.0057 * 1.008
DV
+ 1.0125 * 1.008
1.008
BE
7
b 300 mA + b 7 mA ( 1 ) e )
e + D b b and b + b ( 7mA )
TD
+ nKT
TD
I
1.008
C
1.008
is in °C.
= 100°C.
q
+ I
E
273.15 Kelvin ) T TD
1n
b ( b ) 1 )]
( 1 ) e )
MIN
b
( 1 ) e ) b ) 1
TYPICAL
(b)
with Collector Currents
273.15 Kelvin ) 100° C
273.15 Kelvin ) 100° C
and n
300
BE
, to include the ideality
b ) 1
MAX
= 1.008; any deviation
I
C
nb
(mA)
of a Pentium III
I
C
N
+ * 0.85° C
+ ) 1.67° C
=
b+1
b
I
E
(eq. 4)
(eq. 5)
(eq. 6)
(eq. 7)
(eq. 8)
I
E